1. Technical Field
The present disclosure relates to a radar device using a millimeter waveband or the like and an interference suppression method. More specifically, the present disclosure relates to a technique for preventing or suppressing radio wave interference that occurs in a case where a radar device mounted in a host vehicle and a radar device mounted in another vehicle that is present around the host vehicle use the same radio frequency band (frequency channel).
2. Description of the Related Art
One example of a conventional radar interference prevention method is a method for preventing interference by determining whether or not a host vehicle and another vehicle are positioned so as to interfere with each other through exchange of information, such as a running position or a used radio frequency, between the host vehicle and the other vehicle and then switching the used radio frequency in a case where it is determined that the host vehicle and the other vehicle are positioned so as to interfere with each other (see, for example, Japanese Unexamined Patent Application Publication No. 2010-48716).
Another example of a radar interference prevention method is a method for alternating transmission of a signal (priority order signal) indicative of a priority order relative to another station and transmission of a radar signal (see, for example, Japanese Unexamined Patent Application Publication No. 2007-263915). In this method, in a case where interference is detected by transmission of a priority order signal from another station, a priority order is extracted by specifying an instantaneous frequency on the other station side, and interference is prevented by shifting a frequency band or a transmission timing in accordance with the extracted priority order.
In Japanese Unexamined Patent Application Publication No. 2010-48716, it is necessary to acquire positional information of a host vehicle and another vehicle in order to determine whether or not the host vehicle and the other vehicle are positioned so as to interfere with each other. However, there are places (e.g., an indoor parking lot) where it is difficult to acquire positional information. Furthermore, in Japanese Unexamined Patent Application Publication No. 2010-48716, a radio transceiver unit or the like need be provided in addition to a radar transceiver unit in order to transmit information such as positional information or a used radio frequency. This results in an increase in cost.
In Japanese Unexamined Patent Application Publication No. 2007-263915, interference temporarily occurs because an interference preventing process is started after interference is detected by transmission of a priority order signal from another station. Furthermore, Japanese Unexamined Patent Application Publication No. 2007-263915 assumes that interference can be properly detected even in a complicated radio propagation environment in which an enormous number of multipath waves are present, and therefore requires high interference detection performance. Furthermore, in Japanese Unexamined Patent Application Publication No. 2007-263915, a host station and another station are unable to transmit a radar signal while the host station and the other station are transmitting a priority order signal. This decreases use efficiency of a radio frequency, which is a limited resource.